Process for rendering titanium minerals and ores soluble in acids



United States Patent Ellis E. Creitz, Tuscaloosa, Ala., and Henry G. Iverson, Minneapolis, Minn.

No Drawing. Application June 9, 1952,

1 Serial No. 292,596

7 Claims. (Cl. 23-51) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to us of any royalty thereon in accordance with the provisions of the act of April 30, 1928 (Ch. 460, 45 Stat. L. 467).

This invention relates to a process for treating titanium minerals and ores and more particularly to a process for rendering diflicultly soluble titanium minerals soluble in acids. I

Large deposits of ores containing titanium in various mineral forms ''xist throughout the world. Where the titanium exists in the ore in the form of ilmenite it is readily recoverable from the ore by acid leaching processes. However, in many titanium ores, such as those found in abundance in Florida and other parts of the world, the titanium occurs in the form of rutile, leucoxene, and'other acid insoluble or difiicultly soluble minerals. Rutile and leucoxene are almost completely insoluble in acids under the leaching conditions employed with ilmenite. Some ores contain titanium in the form of acid soluble and acid insoluble titanium materials.

In order to economically treat these ores it has been the practice to separate the soluble titanium minerals from the less soluble titanium minerals prior to acid leaching. Separation operations, however, also are costly and time consuming and a large portion of the titanium in the ore is rejected.

Accordingly, an object of this invention is to prov de a process for rendering difiicultly soluble titanium minerals soluble in acids.

Another object of this invention is to provide a process for converting acid unreactive titanium minerals, such as rutile and other difiicultly soluble minerals, to acid soluble compounds or complexes.

A further object of this invention is to provide a process for converting titanium-bearing non-ilmenitic material, such as rutile and others, to material hav1ng t he same X-ray pattern and substantially the same solubillty characteristics as ilmenite.

A still further object of this invention is to provide a process for converting difficultly soluble forms of titanium in mixtures with more soluble forms of titanium to a more soluble form of titanium whereby substantially the entire titanium content of the mixture may be recovered by acid leaching.

Other objects of the invention will appear from the following description and claims.

These objects are accomplished by heating the titanium minerals or materials in finely divided form with iron minerals or iron compounds, either naturally occurring with the titanium minerals or added thereto, with or without coke or other carbonaceous material, in a substantially non-oxidizing atmosphere or slightly reducing atmosphere containing carbon dioxide. By this method 2,750,255 Patented June 1 2, 1956 "ice 2 to 98 percent of the TiOz in the difficultly soluble titanium. minerals is rendered soluble in acids, as compared to 15 percent or less without such treatment.

According to one embodiment of the invention a finely ground mixture, preferably minus 200 mesh, of the unreactive titanium minerals and iron minerals or compounds, with or without coke, is sintered at a tempera; ture Within the range of from about 2100 F. to about 2500 F., in a substantially non-oxidizing atmosphere for a period of time usually less than 45 minutes and preferably for a period of from about 10 to 30 minutes. The sinter is cooled substantially without ,contactwith air by immediately quenching it in water upon withdrawal from the furnace. The cooled sinter is broken into fine particle and is leached with an acid in a manner commonly known to those familiar with the art.

Suitable iron minerals or compounds for admixture with the titanium-bearing material are siderite, magnetite, titaniferous magnetite, hematite, limonite, FeS, pyrites, and others. Siderite or other minerals containing iron in ferrous form may be employed without coke in the sintering process. Materials containing iron in higher valence forms such as magnetite, limonite, and hematite, require addition of coke or other carbonaceous material to the admixture for best results. In someinstances a small amount ,of FeS may alsobe included .with the higher valence forms of iron and with the. carbonaceous material to further improve the solubility of the titanium in the resulting sinter. v p Although applicants are not bound by any theory of operation, it would appear that the iron in the minerals or compounds is in a reduced form, probably the ferrous form, or is converted to such form under theconditions of the process, in order for the solid reaction between the titanium minerals and the iron minerals .or compounds to take place. The solid reaction occurring during the heating period apparently involves the combining of elemental iron or iron oxide with the titanium minerals in a chemical combination. Titanium material formed in the process exhibits both the X-ray patterns and solubility characteristics of ilmenite. Thus, the invention affords a method for producing synthetic ilmenite from ru'tile and other diflicultly soluble titanium minerals.

From the above discussion, however, it is not to be construed that the high solubilities of TiOz in the product are necessarily limited to the formation of only ilmenite, or material having identical X-ray patterns to that of ilmenite. Good solubilities of TiOz are obtained on products which, by X-ray analysis, contain only approximately 10 to' 20 percentof material giving the X-ray pattern of ilmenite and 20 to percent of material giving the X-ray pattern of hematite or distorted hematite 'or magnetite. v i

The iron minerals or materials in the admixture of titaniferous material to be heat treated should be present in such proportions as to yield a product having a TiO: to Fe weight percent ratio in the range of from .approximately one to four, i. e., 1 TiOz to 1 Fe to 4 TiOz to 1 Fe. Where the titanium ore contains iron within these limits noiron addition is necessary, although coke or other carbonaceous material may be added if it is necessary to convert the iron in the titaniferous ore to ferrous form. Where the iron content of the ore is below that required by the stated ratios, adjustment is made by the addition of ironcontaining material such assiderite, magnetite, hematite, limonite, and othersas mentioned above.

The. particle "size of the material to be heat treated is an important factor in solubilizing the TiOz. In general the raw materials, both titanium material and ironbearing materials, should be ground to pass through a 200 mesh screen and in some instances .to pass through a 325 mesh screen. The raw materials are ground separately or may be admixed and ground together. Coarser ground materials generally require higher temperatures, longer heating periods, or both to effect the same degree of con version as when finer ground materials are used. After the heat treatment, the material may be reground to the same fineness as the original material prior to leaching with acids. However, grinding of friable sinters may be unnecessary as the porosity of the unground sinters permits a relatively high extraction of TiOz by acid leaching.

Although temperatures within the range of about 2100 F. to 2500 F. are preferred in carrying out the process of this invention, the temperatures are not limited thereto. Increase in the solubility of the titanium material may to some extent be realized by heating anywhere within the broad range of from above 200 F. up to that temperature at which the particular materials being treated will melt during the heating period, depending upon other conditions during the heating period. The solubility of the TiO2 in the product will vary depending upon the amount of time the material is exposed to heat, the fineness of the particles of materials heated, the nature of the particular titanium and iron bearing materials being heated, the amount of admixed materials, and the type of admixtures employed. In general, the material should be heated at such temperature and for such a period of time as to form a sintered product. Hence, temperatures outside the preferred limits may be effective in rendering the TiOz in the product soluble in acids so long as the sintering or heating periods, and the fineness of the materials and other controlling conditions are properly adjusted. For example, with some difficultly soluble titanium materials or admixtures, flash heating at extremely high temperatures of 3000 F. or more for a few seconds or for a few minutes may give equally good results as those obtained at 2200 F. with minute sintering periods. Also, excellent solubilities may be obtained of the TiOz in sinters prepared from the same materials in the same manner, but sintered or heated at furnace temperatures lower than 2200 F. for longer periods of time, for example, from a few hours to 24 hours or more. A 20 to minute sintering period at temperatures within the range of 2100 F. to 2500 F. results in a product having a high TiOz solubility, when other conditions as set forth herein are observed.

The heating or sintering should be conducted in an atmosphere containing carbon dioxide. Slightly reducing conditions are beneficial. Sintering under oxidizing conditions, as in air, decreases the solubility of TiOz in the product. A slightly reducing atmosphere containing CO2, with or without some carbon monoxide and minor amounts of oxygen, suitable for the purposes of this invention, can be readily maintained in commercial furnaces fired with artificial or natural gas, coal, coke or other carbon-containing fuels. In electric furnaces CO2 from any suitable source may be passed over the charge being heated. Absolute absence of oxygen or air is unnecessary provided the atmosphere is predominantly CO2 or is slightly reducing.

At the end of the sintering period the material is withdrawn from the furnace and is quickly quenched in water. This treatment is applied to avoid re-oxidation of the material. Other means, such as cooling in inert or reducing atmosphere, may be used in lieu of quenching.

The invention is further illustrated but is not limited by the following examples of practice. In carrying out the process in these examples, the samples were placed in open fire clay or ceramic dishes, which in turn were placed in a tube furnace that had been preheated to the temperature at which the material were to be sintered. The atmosphere used in sintering was commercial carbon dioxide passed into the interior of the furnace in contact with the material being sintered. At the end of the sintering period the samples were withdrawn from the furnace and quickly quenched in water. The solubility of the TiOz in the products was determined by sulfating and leaching the product and calculating the percentage recovery of TiOz in the leach solution as compared with the percentage of TiOz in the heat treated product, in a manner familiar to those practiced in the art.

The following Examples 1 and 2 give the percentage of TiOz solubilized in mixtures of difficultly soluble titanium minerals containing rutile, leueoxene and others, and ilmenite, by direct leaching and by sintering in CO2 atmosphere without admixtures.

Example 1 Material containing about 79 percent TiOz and 12 percent iron was ground to minus 325 mesh and leached with 90 percent sulfuric acid. Only 52 percent of the total TiOz was solubilized.

Example 2 Similar material, fineness, and treatment as in Example 1, except that the ground minus 325 mesh material was sintered without any admixtures for 20 minutes at 2200 F. in CO2 atmosphere and the sinter crushed through 48 mesh before leaching. Only 25 percent of the total TiOz was solubilized.

Example 3 This gives the resulting effects, as compared with Examples l and 2, of sintering similar material as used in Examples 1 and 2, also ground to minus 325 mesh but mixed with siderite in the proportions of 6 parts titanium Example 4 This consisted of several tests utilizing material similar to that in Examples 1, 2, and 3. The tests were conducted in the same manner and under the same conditions as given in Example 3 except that the proportions of siderite to the titanium minerals were varied.

- i Percent sintering conditions Percent Parts of Parts of total siderite g mmera s so u i Tune, Temp, Atmosminutes F. phere Fe T10:

6 2 20 2, 200 C On 21 65 62 6 2% 2O 2, 200 O ()2 23 65 67 6 3 20 2, 200 C O: 25 60 7S 6 3% 20 2, 200 C02 27 58 6 4 20 2, 200 C02 28 55 85 6 4% 20 2, 200 CO: 29 54 91 6 5 20 2, 200 G 0: 30 52 91 The data in the above example show how the solubility of TiOz in the sinter increased, under the conditions of trial, with increasing amounts of siderite up to 4 /2 parts, with 6 parts of titanium minerals.

Example 5 Rutile containing about 96 percent TiOz and about 1 percent iron was ground to minus 325 mesh and leached directly with percent sulfuric acid. Only about 15 percent of the total TiOz was dissolved.

Example 7 Rutile as used in Examples 5 and 6 was ground to minus 325 mesh and mixed with minus 325 mesh siderite in the proportion of 6 parts of rutile to 8 parts of siderite, sintering the mixtures for 20 minutes at 2200 F. in CO2 atmosphere. Ninety-two percent of the total TiOz in the ground sinter was now soluble in 90 percent sulfuric acid, contrasted to the 15 and 10 percent solubilities in Examples 5 and 6.

Example 8 This consisted of several tests utilizing rutile similar to that used in Examples 5, 6, and 7. The tests were conducted in the same manner and under the same conditions as given in Example 7, except that the proportions of siderite to rutile were varied. All sinters were crushed through 48 mesh before leaching in 90 percent sulfuric acid.

Percent in sintering conditions Percent Parts Parts sinter of total rutile ki T1102 1 e so ulime, Temp. Atmosminutes F. phere Fe humid 6 3 20 200 C02 17 72 .45 a G 5 20 2, 200 C 01 23 62 70 6 7 20 2, 200 C02 27 55 82 6 8 20 2, 200 C02 31 49 92 6 8% 20 2, 200 C02 32 44 90 Y The data in the above example show how the solubility of the TiOz in 90 percent sulfuric acid increased, under the conditions of trial, with increasing amounts of siderite up to 8 parts of siderite to 6 parts of rutile. The maximum amount of TiOz dissolved was 92 percent.

Example 9 Sinterlng conditions i gg Percent Parts Parts of total rutile sider- TiIOn 1 e so u- Tnne, Temp., Atmosminutes phere Fe T10: bllized 6 8 20 2, 200 CO: 31 49 92 6 8% 20 2, 200 C02 32 48 90 6 7 30 2, 200 CO: 29 53 87 6 8 30 2, 200 C02 31 50 93 6 8% 30 2, 200 C01 32 49 98 6 7 40 2, 200 C 02 29 54 91 6 8 40 2, 200 O 02 31 51 98 6 8% 40 2, 200 C02 33 60 98 The above data showed that sintering mixtures of rutile and siderite for periods of 30 or 40 minutes under the conditions of trial may be advantageous, compared to the 20-minute sintering period, in that less siderite may be used for making equal or more soluble sinter, higher in TiO2 content.

. Example 10 This consisted of several tests utilizing rutile similar to that used in Examples 5 to 9, inclusive. The tests show the effects of using the following admixtures with rutile: magnetite;; coke and magnetite; FeS, coke, and magnetite; and sintering at 2200 F. and 2300 P. All materials were ground to minus 325 mesh before sintering for 20 minutes in COzatmosphere. All sinters were crushed through 48 mesh before leaching in 90 percent sulfuric acid.

Parts admixtures fiigg Percent Parts sintering of total temp., Ti02 Ma F. solubil- 'Coke res Fe T102 ized 6 5% 2,200 51 25 6 15% 2,200 35 51 31 1 a 4 2g 5 2,200 as 54 87 '6 5% 2,300 s5 s2 s 1 34 2,300 as 54 89 s I 4 2,300 35 a5 88 From the above datait is evident that sintering rutile with magnetite at either 2200 or 2300 F. for 20 minutes did not render the TiOz in the sinter highly soluble. The use of /2 part of coke under the conditions of trial did not materially affect the solubility of the TiOz at 2200 F., but greatly increased the solubility at 2300 F. Compared with admixtures of coke and magnetite, the use of A: partof FeS with /2 part coke and 5 parts magnetite, with 6 parts rutile, was markedly effective in greatly increasing the solubility of TiOz in the sinter prepared at 2200 F., but was not more effective than coke at 2300 F.

Example 11 This consisted of several tests utilizing rutile similar to that used in Examples 5 to 10, inclusive. They give the effects of using the following admixtures with rutile: Hematite; coke and hematite; FeS, coke, and hematite; and sintering at 2200 F. and 2300 P. All materials were ground to minus 325 mesh before sintering in CO2 atmosphere. Sintering period for all tests was 20 minutes. All sinters were crushed through 48 mesh before leaching in 90 percent sulfuric acid.

' Percent Parts admixtures Smtering m sinter Percent Parts of total rutile H T At Tligz stalemaemp., mosu i ize Ooke FeS me o phere Fe T10 6 5% 2, 200 C02 35 50 14 6 5% 2, 200 0 O 33 61 8 6 5 2, 200 C02 34 54 91 6 5% 2, 300 O0, 33 51 24 6 5% 2, 300 CO: 34 54 83 6 56 5 300 C02 34 54 From the above data it is evident that sintering rutile with hematite at either 2200 F. or 2300 F. for 20 minutes did not render the TiOz in the sinter highly soluble. The use of A: part of coke under the conditions of trial did not materially affect the solubility of the TiOz at 2200 F., but greatly increased the solubility at 2300 F. Compared with admixtures of coke and hematite, the use of /2 part of FeS with /2 part coke and 5 parts hematite, with 6 parts rutile, was very effective in increasing the solubility of TiOz in the sinter prepared at 2200 F., but was not markedly effective at 2300 F.

Example 12 This consisted of several tests utilizing rutile similar to that used in Examples 5 to 11', inclusive, using the following admixtures with rutile: limonite; coke and limonite; FeS coke, and limonite; and sintering at 2200 F. and 2300 F. All materials were ground to minus 325 mesh before sintering in CO2 atmosphere. Sintering period for all tests was 20 minutes. All sinters were crushed through 48 mesh before leaching in 90 percent sulfuric acid.

Parts admixtures Sintering 52%;; Percent Parts oftotal rutile LY T I ,At T%)( )1zf'SO(11- memp., mosu 1 ze Coke FeS nice 0 F. phere Fe T101 6 6 2,200 001 31 52 16 6 A 6 2,200 00: 31 24 6 5% 2,200 00: 32 55 89 6 6 2, 300 C0: 31 53 27 6 6 2, 300 C02 31 55 88 6 V2 5% 2,300 G01 31 55 91 From the above data it is evident that sintering rutile with limonite at either 2200 F. or 2300 F. for 20 minutes did not render the TiOz in the sinter highly soluble. The use of /2 part of coke under the conditions of trial did not materially aiiect the solubility of the TiOz at 2200 F., but greatly increased the solubility at 2300 F. Compared with admixtures of coke and limonite, the use of V2 part FeS with /2 part coke and 5 /2 parts limonite was very effective in increasing the solubility of the TiOz in the 8 material ground to minus 325 mesh than in material ground to minus 200 mesh. With the finer material, the 2200 F. temperature was as 'eifectiv'e as 23 0 0 F. in rendering an equally high amount of TiO-z soluble.

Example 14 This includes several tests which give the sintering conditions under which titanium minerals, mixed with admixtures, were converted to ilmenite. The determinations of the mineral contents in the sinters were made from X-ray powder-patterns of the products. Sintering conditions that were the same for all tests shown were: temperature, 2200 F.; atmosphere, CO2. Ninety percent sulfuric acid was used in determining the solubiliti es of the TiOz in the sinters. Two types of titanium-containing materials were used, namely, rutile containing about 96 percent TiOz and 1 percent iron, and a mixture of difficultly soluble titanium minerals similar to that used in Example 13. The rutile and admixtures were ground to minus 325 mesh before sintering. For the first sinte'r'i'ng test shown on the mixture of titanium minerals, the material was ground to minus 200 mesh, and for the second test, to minus 325 mesh. No admixture was used in sintering the mixture of titanium minerals.

Percent in Percent Percent inrsinter determined Titanium materials Parts Sintersinter of total from X-ray patterns admin, ing TiOa siderite time solu- Material Parts Fe T10: bilized llmenite Rutile Others 6 0 26 l 97 1o 100 6 7 20 27 55 84 90 trace trace. 6 8% 30 32 49 98 95 trace. Not sintered 22 49 65 20 Zircon and T10: mineral mixtures- No admix. 20 23 49 90 9'5 trace No admix. 20 24 47 96 95 trace sinter prepared at 2200 F., but was not markedly eifecm The data in the above table show that sintering rutile tive at 2300 F. Example 13 This consisted of several tests which show that, on materials containing diflicultly soluble titanium minerals and iron compounds in amount adequate to form soluble ti- 45 tanium-iron compounds, the solubility of the TiOz in such diflieultly soluble mixtures may be greatly increased by merely heating the ground materials without any admixtures at elevated temperatures for short periods of time in CO2 atmosphere. The titanium material involved in the 56 tests contained about 46 to 49 percent T102 and 22 to 24 percent Fe. All sinters were crushed through 48 mesh before leaching in 90 percent sulfuric acid. Test conditions and results are given in the following table:

Material not sintered, hence, analyses and percent of soluble T102 are given for original material.

Only to 66 percent of the total TiOz in the material ground to minus 200 and minus 325 mesh was soluble in 90 percent sulfuric acid. At the same finenesses, the solubility of the total TiO-z was increased to 90 and 96 percent, respectively, by merely heatingthe material without any admixtures to 2200 F. and 2300 F. in CO2 atmospher'e. Somewhat more TiOz was rendered soluble in alone yielded very low solubility of TiOz in the sinter and that thesinter contained only rutile. However, sintering under identical conditions a mixture of 6 parts rutile and 7 parts siderite greatly increased the solubility of the TiOz in the sinter, and percent of the material in the sinter consisted of ilmenite or material which had the same X-ray pattern as ilmenite. Increasing the amount of side'rite and sintering time resulted in a further increase in the solubility of TiOz and in the amount of ilmenite in the sinter.

The mixture of titanium minerals consisting of 50 percent ilmenite and 20 percent rutile was almost wholly converted to ilmenite by merely heating to 2200 F. for 20 minutes iii COi atmosphere.

Example 15 Sir'iterin Mesh of Percent g 2322i? s, $253535 $5 ru 1 e an I l 1 so admlx' rutile $2 3,? ubilized (i 7 -325 2, 200 C02 55 S2 The finer material, minus 400 mesh, required less siderite and a lower temperature to yield TiOz solubilities in the sinter comparable to those obtained on the coarser material with more siderite and higher temperature. With equal amounts of siderite, however, and 2200 F., the

10 2. A process for converting diflicultly soluble titanium minerals to acid-soluble form comprising grinding the titanium minerals to pass a 200 mesh screen, mixing the finely divided titanium minerals with a finely divided ironsolubiiities of the TiO in sinters prepared from minus bearing material in which iron is present in a higher 200 mesh material were equal to those from sinters prevalence form, to provide a TiOz to Fe weight ratio within pared from minus 325 mesh material. the range of from about one to about four, adding car- From the above example and the foregoing examples, it bonaceous material to the admixture, sintering the admixis evident that the fineness of the material to be sintered, ture at a temperature of about 2300 F. for at least the amount and type of admixtures added, the amount 10 minutes in a substantially non-oxidizing atmosphere conand type of titanium minerals to be treated, the length of taining carbon dioxide, and quenching the sintered sintering periods, and the optimum sintering temperatures material. are factors that are all interrelated and interdependent, one 3. The process of claim 2 in which the iron-bearing on another. Being thusly interrelated, any one of the mat rial iS mag t tefactors may be varied somewhat in forming high amounts 4. The process of claim 2 in which the iron-bearing of soluble TiOz in the sinters. material is hematite.

Example 16 5. Tkie process of claim 2 in which the lron-bearmg materia is imonite. A 20 minerals to acid soluble form comprising grmdlng the containing materlal similar to that used in Example 13 was t1tan1um minerals to pass a 200 mesh screen, mixing the mixed in the proportion of 6 parts titanium materlal to 1 h b part siderite, and placed in open crucibles or ceramic fine,ly d1v1de d t1 tamu m mmemis f, an Iron' earmg madishes, and heated to various temperatures in a rnufile furtena! whlfih IS Preent 1n f i valence form to nace while exposed to air. As was shown in Example 13, Provlde a T102 to Fe Welght r m the range of q 65 percent of h Tio could b leached f the about one to about four, adding carbonaceous material treated material; and by merely heating the material in and F65 t0 the admixtum, sintefil'lg the admixture at a C02 atmosphere to 2200 F., a high solubility of the TiOz temperature of from about 2100 F. to about 2500 F. for in the sinter was obtained. at least 10 minutes in a substantially non-oxidizing atmos- Minerals in sinter detd Riga Parts of Temp Sinter- Percent Et {mm patterns mineral iifiii" tniii Etta 8538i ized 13 Rutile Egg 6 1 390 20 40 65 x x x s 1 760 20 41 as x x x e 1 1,200 20 43 36 x x x 6 1 1, 560 20 43 29 x x 6 1 1, s40 20 43 27 x x Despite the beneficial presence of some siderite phere containing carbon dioxide, and quenching the sin- (FeCOs) from which CO2 would be evolved at the higher tered material. temperatures, the ilmenite contained in the original ma- 45 7. A process for converting rutile to material having terial was entirely converted to rutile at 1560 F. There substantially the same X-ray pattern and solubility charwas also a considerable increase in the amount of hematite acteristics as ilmenite comprising admixing finely divided with increasing temperature due to the disassociation and rutile with finely divided siderite in proportions to provide oxidation of the iron oxide from the ilmenite. a TiOz to Fe Weight ratio in the range of from about one Since many widely differing embodiments of the invento about four, sintering the admixture in an atmosphere tion will occur to one skilled in the art, the invention is of Carbon dioxide at a temperature of about 2200 for not limited to the specific details ilIilstrated and described, about 20 minutas, and quenching the sintered P and various changes may be made therein without depart- References Cited in the file of this patent mg from the spirit and scope thereof.

What We claim UNITED STATES PATENTS 1. A process for converting difficultly soluble titanium 2,197,085 Stuart Apr. 16, 1940 minerals to acid-soluble form comprising grinding the 2,375,268 WyckOfi? May 5 titanium minerals to pass a 200 me h r i i th ,101 Campbell Mar. 11, 1947 finely divided titanium minerals with finely divided iderite 2,445,377 Wyckofi July 20, 1948 to provide an admixture containing TiO a d F i 2,453,050 Turkett 2, 1948 We ght ratio Within the range of from about one to about goyster ga fi Sintering the admixed materials at a temperature of 6319 41 fg J g 1953 from about 2100 F. to about 2500 F. for at least 10 OTHER REFERENCES minutes in a substantially non-oxidizing atmosphere containing carbon dioxide, and quenching the sintered material.

Metals Transactions, vol. 185, December 1949, pages 92%914, article by Cole et al., Ti Dig. 

1. A PROCESS FOR CONVERTING DIFFICULTLY SOLUBLE TITANIUM MINERALS TO ACID-SOLUBLE FORM COMPRISING GRINDING THE TITANIUM MINERALS TO PASS A 200 MESH SCREEN, MIXING THE FINELY DIVIDED TITANIUM MINERALS WITH FINELY DIVIDED SIDERITE TO PROVIDE AN ADMIXTURE CONTAINING TIO2 AND FE IN A WEIGHT RATIO WITHIN THE RANGE OF FROM ABOUT ONE TO ABOUT FOUR, SINTERING THE ADMIXING MATERIALS AT A TEMPERATURE OF FROM ABOUT 2100* F. TO ABOUT 2500* F. FOR AT LEAST 10 MINUTES IN A SUBSTANTIALLY NON-OXIDIZING ATMOSPHERE CONTAINING CARBON DIOXIDE, AND QUENCHING THE SINTERED MATERIAL. 